制备Mo_2C催化剂的最佳工艺条件及其反应机理

Optimum Process Conditions and Reaction Mechanism of Preparing Mo_2C Catalyst

钼酸铵焙烧制备碳化钼前驱体MoO3,以MoO3为钼源、V(H2)/V(CH4)混合气体为碳化介质采用程序升温反应法制备Mo2C催化剂;考察钼酸铵制备MoO3适宜的温度,以及程序升温反应法制备Mo2C的最适V(H2)/V(CH4)比和碳化终温,用XRD表征分析产物。得出制备Mo2C催化剂的最佳工艺条件是:钼酸铵焙烧温度为450℃、V(H2)/V(CH4)为2︰1～4︰1、碳化终温为700℃;其反应机理是:MoO3先被还原为MoO2,MoO2需经历过渡态的单质Mo才能碳化生成Mo2C。

Molybdenum trioxide as precursor was prepared by roasting ammonium molybdate.Then using molybdenum trioxide and the gas mixture of H2 and CH4 as raw materials,molybdenum carbide was prepared by the temperature-programmed reaction method.The best temperature of preparing molybdenum trioxide from ammonium molybdate was investigated as well as the best ratio of H2 to CH4 and terminal temperature in the temperature-programmed reaction;the final product was characterized by X-ray diffraction.The results show that the optimum process conditions for the reaction： roasting temperature is at 450 ℃,V（H2）/V（CH4） is in the range of 2︰1～4︰1,the final temperature of carbonization is at 700 ℃;the reaction mechanism： firstly,MoO3 is reduced to MoO2,then MoO2 must be reduced to transition state Mo,finally Mo2C is gained.